Classification of birds and drones by exploiting periodical motions in Doppler spectrum series

With the rapidly growing abuse of drones, monitoring and classification of birds and drones have become a crucial safety issue. With similar low radar cross sections(RCSs), velocities, and heights, drones are usually difficult to be distinguished from birds in radar measurements. In this paper, we propose to exploit different periodical motions of birds and drones from highresolution Doppler spectrum sequences(DSSs) for classification.This paper presents an elaborate feature vector representing the periodic fluctuations of RCS and micro kinematics. Fed by the Doppler spectrum and feature sequence, the long to short-time memory(LSTM) is used to solve the time series classification.Different classification schemes to exploit the Doppler spectrum series are validated and compared by extensive real-data experiments, which confirms the effectiveness and superiorities of the proposed algorithm.

Estimation of sea clutter inherent Doppler spectrum from shipborne S-band radar sea echo

Measurement of shipborne radar sea echo is instrumental in collecting the sea clutter data in open sea areas.However,the ship movement would introduce an extra Doppler component into the spectrum of the sea clutter,so the sea clutter inherent spectrum must be estimated prior to investigating the sea clutter Doppler characteristics from the shipborne radar sea echo.In this paper we show some results about a shipborne sea clutter measurement experiment that was conducted in the South China Sea in a period between 2017 and 2018;abundant clutter data have been collected by using a shipborne S-band clutter measurement radar.To obtain the sea clutter inherent Doppler spectrum from these data,an estimation method,based on the mapping relationship between the shipborne clutter spectrum and the inherent clutter spectrum,is proposed.This method is validated by shipborne clutter data sets under the same measuring conditions except for the ship speed.Using this method,the characteristics of the Doppler spectrum lineshapes in the South China Sea are calculated and analyzed according to different sea states,wave directions,and radar resolutions,which can be instrumental in designing the radar target detection algorithms.

An ocean current inversion accuracy analysis based on a Doppler spectrum model

Microwave remote sensing is one of the most useful methods for observing the ocean parameters. The Doppler frequency or interferometric phase of the radar echoes can be used for an ocean surface current speed retrieval,which is widely used in spaceborne and airborne radars. While the effect of the ocean currents and waves is interactional. It is impossible to retrieve the ocean surface current speed from Doppler frequency shift directly. In order to study the relationship between the ocean surface current speed and the Doppler frequency shift, a numerical ocean surface Doppler spectrum model is established and validated with a reference. The input parameters of ocean Doppler spectrum include an ocean wave elevation model, a directional distribution function, and wind speed and direction. The suitable ocean wave elevation spectrum and the directional distribution function are selected by comparing the ocean Doppler spectrum in C band with an empirical geophysical model function（CDOP）. What is more, the error sensitivities of ocean surface current speed to the wind speed and direction are analyzed. All these simulations are in Ku band. The simulation results show that the ocean surface current speed error is sensitive to the wind speed and direction errors. With VV polarization, the ocean surface current speed error is about 0.15 m/s when the wind speed error is 2 m/s, and the ocean surface current speed error is smaller than 0.3 m/s when the wind direction error is within 20° in the cross wind direction.

Doppler Spectrum Analysis of Time-Evolving Sea Surface Covered by Oil Spills

Based on the model of a contaminated sea surface that was proposed by Lombardini et al., the influence of the damping effect of oil films on the sea surface roughness spectrum and the geometrical structure of the sea surface is examined in detail by comparing with a clean sea surface. Fhrthermore, based on a quasi-stationary algorithm, a time series of backscattered echoes from a time-evolving sea surface covered by oil slicks is obtained by utilizing the frequency-domain numerical method of the parallel fast multiple method. Then, the Doppler spectrum is evaluated by performing a standard spectral estimation technique. Finally, the influence of the oil film damping effect on the Doppler spectrum of the backscattered echoes from time-evolving sea surface is investigated in detail by making a comparison of the Doppler spectrum of an oil-covered sea surface with the Doppler spectrum of a dean sea surface. The numerical simulations show that the damping effect of oil films has an influence on the Doppler spectrum signature for both horizontal-to-horizontal and vertical-to-vertical polarizations.

Numerical simulation of the EM scattering and Doppler spectrum of a low flying target above dynamic oceanic surface by using the FEMDDM method

To study the Doppler (DP) spectrum of a flying target above the dynamic oceanic surface, a two-level quasi-stationary algorithm (TLQSA) of the finite element method (FEM) with domain decomposition (DDM) is developed. The DP spectrum of a fast-moving target requires a small time-sampling rate. At most time steps, scattering from the flying target is solved by the FEM solution in only one sub-domain; meanwhile the interactions between the target and rough sea surface in other sub-domains are obtained by solving the global DDM coupling matrices. The slowly moving sea surface is evolved at a larger time step and the DP of oceanic clutter is obtained through all-subdomain FEM calculation. Numerical simulations of the DP spectrum from a target flying above the dynamic oceanic surface with and without a ship presence are obtained. The functional dependence of the DP spectrum in both the time and frequency domains upon the sea surface wind speed, target altitude, observation angle etc. are demon- strated and discussed.

Study on electromagnetic backscattering and Doppler spectrum of a moving spherical target above time-varying sea surface

The surface electric current of the sea surface and the first-order scattering field from the spherical target were obtained by employing Physical Optics method and Mie theory,respectively. The backscattering field of the time-evolving sea surface was calculated by using Kirchhoff Approximation. Meanwhile,by taking the ad-vantage of a newly developed technique that utilizes the reciprocity theorem,the difficulty in formulating the secondary coupling scattering fields from the spherical target above the sea surface was reduced. The dependence of the secondary cou-pling backscattering field on the size and the position of the spherical target was discussed,and the characteristic of the Doppler spectrum of the composite back-scattering field with different incident angles was analyzed in detail.

二维斑点追踪技术在评估冠心病患者左心室收缩与舒张功能中的应用价值

目的探讨二维斑点追踪技术在评估老年冠心病患者左心室收缩与舒张功能中的应用价值。方法对60例老年冠心病患者(研究组)和60名健康老年人(对照组),应用彩色多普勒超声诊断仪进行左心室功能检查。比较两组血压、生化指标(三酰甘油、高密度脂蛋白胆固醇、低密度脂蛋白胆固醇、总胆固醇、糖化血红蛋白)及常规超声参数、二维斑点超声应变参数、血流频谱测量超声参数。结果研究组受试者收缩压、舒张压及三酰甘油、高密度脂蛋白胆固醇、低密度脂蛋白胆固醇、总胆固醇、糖化血红蛋白水平均高于对照组(P<0.01)。两组受试者收缩末期和舒张末期的左室内径、室间隔壁厚度、左室前/后/下壁厚度比较,差异无统计学意义(P>0.05)。研究组受试者左室舒张充盈末流速峰值/左室收缩末流速峰值低于对照组(P<0.05);两组受试者左室射血分数、左室舒张充盈末流速峰值、左室收缩末流速峰值比较,差异无统计学意义(P>0.05)。研究组受试者舒张期和收缩期的左心室前壁、后壁、下壁、室间隔的纵向、径向、周向峰值绝对值均低于对照组(P<0.01)。结论二维斑点追踪技术的抗干扰能力较强,二维斑点超声应变参数能有效反映冠心病患者左室收缩、舒张情况,具有较高的应用价值。

融合卫星姿态的星地信道建模及硬件模拟

针对传统星地信道模型及其硬件模拟方法没有考虑卫星姿态对信道特性影响的问题,本文基于几何地理随机模型(Geometry-based Stochastic Model,GBSM)框架,提出了一种融合卫星姿态的星地信道模型。该模型通过构建四个独立的坐标系并引入姿态修正矩阵,来描述卫星姿态变化对星地信道特性造成的影响。在此基础上,本文基于现场可编程门阵列(Field Programmable Gate Array,FPGA),设计并研制了一种星地信道硬件模拟器。硬件模拟器采用差分迭代的算法来生成信道衰落因子,可以极大提高硬件模拟的实时性,确保生成的衰落数据与实际场景相匹配。同时,还采用了并行处理架构,可以支持最大640 MHz带宽的星地信道模拟。为了将衰落数据与并行架构相匹配,引入了并行内插算法,可以将串行的衰落数据内插成同速率的多路并行衰落数据。此外,为了能够精准控制硬件装置输出信号的功率,设计了基于预训练的功率校正方法。通过内部校正源信号预先训练出整个模拟过程给信号带来的增益再进行功率补偿,从而保证输出信号的功率可以被精准控制。最后,在典型场景下开展仿真模拟,导出硬件模拟器的输出结果并分析其统计特性,结果表明实测输出的概率密度函数(Probability Density Function,PDF)和多普勒功率谱密度(Doppler Power Spectral Density,DPSD)与理论值吻合,证明本文设计的硬件模拟器可以准确地复现实际场景下卫星姿态发生变化的星地信道。本文提出的融合卫星姿态的星地信道模型以及研制的硬件模拟器很好地解决了传统模型以及硬件模拟方法的局限性,在卫星通信系统的优化、评估和验证环节具有极大的潜在价值。

大Doppler频移条件下基于导频信号的扩频码捕获

分析了Doppler频移对传统扩频码捕获算法的影响,提出了在发送导频信号期间,利用自适应谱线增强器(ALE)对部分匹配滤波输出进行处理以估计Doppler频移值,经过频偏校正后,采用传统全匹配捕获算法进行扩频码捕获判决的新方法。仿真结果表明,这种方法可以有效地消除大Doppler频移的影响,迅速完成扩频码的捕获。

降水微物理过程的C波段垂直指向雷达反演研究

降水微物理过程是对空中雨滴的蒸发、碰并和凝结等演化过程的最直接描述。对降水过程中微物理特征的分析,有利于提高对云体的认识,为降水估计与数值模式参数化提供技术支撑。研究依托中国气象科学研究院灾害天气国家重点实验室在广东龙门建立的超级观测站,基于C波段调频连续波雷达高时空分辨率的多普勒功率谱数据。分析了2020年6月6-9日(前汛期),受西南季风影响,形成的一次持续时间长、累积雨量大、降水分布不均的降水过程中的几种典型对流单体的空中微物理特征。

Microwave Doppler spectra of sea return at small incidence angles:specular point scattering contribution

It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the incidence angle becomes smaller （≥ 20°）. Here, in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation, analytical expressions for Doppler shift and spectral bandwidth of specular point scattering, which are insensitive to the polarization state, are derived theoretically. For comparison, the simulated results related to the two-scale method （TSM） and the method of moment （MOM） are also presented. It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles. However, a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case. In this work, the dependences of the predicted results on incidence angle, radar frequency, and wind speed are also discussed. The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces.

一种扩展GMSK扩频多普勒捕获范围的方法

伪码捕获在短时猝发GMSK(高斯滤波最小频移键控)扩频通信中是不可缺少的一环,尤其是在接收端弱信号的情况下,多普勒频移会严重影响接收端伪码捕获性能。针对短时猝发GMSK扩频体制的特殊性,设计了接收端伪码捕获算法,推导分析了该捕获算法的相关公式,并在此基础上提出了一种多通道并行接收捕获的方法以适应短时猝发条件,该方法通过扩展多普勒适应范围以提升GMSK扩频通信系统伪码捕获性能,将该方法应用到短时猝发GMSK扩频通信系统中,可提升伪码捕获峰值阈值约2.7 dB以满足系统灵敏度要求,且占用硬件资源较少。

OFDM通信系统中的一种最大Doppler频移估计算法

在分析了已有各种Doppler估计算法的基础上,根据功率谱估计经典算法——窗函数法的原理,直接利用接收到的频域中连续导频信号,进行最大Doppler频移估计。该算法同时适合于单载波和多载波系统。仿真结果均表明:在单径和多径条件下,该算法均可对正交频分复用(OFDM)传输系统中的最大Doppler频移获得较精确的估计结果。该算法十分适合于OFDM移动通信系统。

基于激光多普勒振动谱的数控机床主轴故障在线诊断

针对现有数控机床主轴故障检测算法存在的检测精度低、故障分类效果差等不足,提出一种基于激光多普勒振动谱的在线针对方案。先构建以激光器和探测器为核心部件的激光多普勒故障检测系统,采集故障数据集并对数据进行降维处理;然后针对机床主轴多故障模态的情况,基于可变经验模态分解(VMD)算法分解故障的本征模态分量,形成新的故障特征集;最后利用经过改进的深度卷积神经网络训练故障特征集,实现对多故障模态的分类识别和诊断。实验结果显示,所提算法信号源频率误差值较低,在故障点的诊断和分类识别过程中,效果显著优于传统故障在线诊断算法。

一种短时猝发GMSK扩频多普勒估计算法研究

多普勒估计是猝发传输背景下的GMSK(Gaussian Filtered Minimum Shift Keying,高斯最小频移键控)扩频通信系统接收端同步过程中的关键一环。针对短时猝发GMSK扩频通信系统信息传输时间极短的特点,搭建了系统接收端同步段结构,并以此为基础设计了适应该短时猝发同步段结构的多普勒估计算法,建立了短时猝发多普勒估计算法模型,推导该算法公式的同时对算法模型进行了理论分析,详细阐述了该算法进行多普勒估计的实现过程,并对该算法进行仿真实验。实验结果表明,该算法在信噪比为1 dB时,多普勒估计准确度可达到97.2%,信噪比≥3 dB时,准确度均能在99%及以上,该结果验证了该算法应用在猝发传输背景下的GMSK扩频通信系统中的有效性、可行性,同时也表明当通信系统处于弱信号的条件下时,该多普勒估计算法性能依然能达到一个较为优异的准确度值。

超声测定子宫动脉及多普勒血流频谱在子痫前期中的预测价值及对妊娠结局的影响研究

目的 探讨超声测定子宫动脉及多普勒血流频谱在子痫前期(PE)中的预测价值及对妊娠结局的影响。方法 选取本院接受常规超声检查的1126例孕周≤28周孕妇为研究对象,回顾性分析其临床资料。根据超声检测结果分为高风险组(1071例)和低风险组(55例)。以临床诊断为金标准,比较两组PE发生情况、超声检查结果和妊娠结局。结果 高风险组PE发生率、血流动力学参数水平高于对照组(P<0.05)。高风险组剖宫产、低体质量儿、早产、胎膜早破发生率高于低风险组(P<0.05)。结论 超声测定子宫动脉及多普勒血流频谱在PE中有着较好的预测价值,能为疾病的早期治疗提供依据,以改善妊娠结局,可推广使用。

高动态短猝发扩频自适应信号快捕系统设计

在高动态环境下,短猝发信号传输过程中往往会产生普勒频偏,增加扩频信号的捕获时间,甚至降低信号捕获信噪比,为实现对扩频自适应信号的快速、有效捕获,设计高动态短猝发扩频自适应信号快捕系统;系统硬件采用模块化设计方式,改装信号接收模块和滤波模块,从信号缓存和锁相环两个方面调整系统电路;在硬件系统支持下,通过扩频过程的模拟确定高动态短猝发扩频信号特征,通过特征匹配实现对高动态环境中短猝发扩频信号的自适应搜索;计算捕获长度、频率、门限等参数,实现系统的短猝发扩频自适应信号快速捕获功能;实验结果表明,在无噪声条件下,优化设计系统输出扩频信号信噪比的平均值为141.6,捕获时间平均为8 s,捕获面积平均为90 km^(2);在有噪声条件下,系统输出扩频信号信噪比的平均值为121.8,捕获时间为10 s,捕获面积为130 km^(2)。

Comprehensive wind correction for a Rayleigh Doppler lidar from atmospheric temperature and pressure influences and Mie contamination

A correction considering the effects of atmospheric temperature, pressure, and Mie contamination must be performed for wind retrieval from a Rayleigh Doppler lidar（RDL）, since the so-called Rayleigh response is directly related to the convolution of the optical transmission of the frequency discriminator and the Rayleigh–Brillouin spectrum of the molecular backscattering. Thus, real-time and on-site profiles of atmospheric pressure, temperature, and aerosols should be provided as inputs to the wind retrieval. Firstly, temperature profiles under 35 km and above the altitude are retrieved, respectively,from a high spectral resolution lidar（HSRL） and a Rayleigh integration lidar（RIL） incorporating to the RDL. Secondly,the pressure profile is taken from the European Center for Medium range Weather Forecast（ECMWF） analysis, while radiosonde data are not available. Thirdly, the Klett–Fernald algorithms are adopted to estimate the Mie and Rayleigh components in the atmospheric backscattering. After that, the backscattering ratio is finally determined in a nonlinear fitting of the transmission of the atmospheric backscattering through the Fabry–Perot interferometer（FPI） to a proposed model.In the validation experiments, wind profiles from the lidar show good agreement with the radiosonde in the overlapping altitude. Finally, a continuous wind observation shows the stability of the correction scheme.

C-V2X系统中动态信道预测的R-ATB算法

在智能交通系统中,由于车辆节点高速运动,且速度、方向等状态频繁发生变化,造成了车联网无线信道的时变衰落.针对目前所采用的自适应交通信标ATB(adaptive traffic beacons)预测算法过程较为复杂、使用信道质量评估指标较多的问题,提出了新型的R-ATB预测算法.根据节点运动的多普勒频移程度,计算对应的相关时间参数RT(relevant time),给出R-ATB算法.通过OMNET++通用网络平台的条件设定与系统建模,对相关信道预测算法下的PDR(package delivery rate)与时延参数进行分析与评估.结果表明:与静态信标和传统ATB算法相比,R-ATB预测算法使用较少的实时评价指标量与较小的预测过程计算量,降低了IoV的通信信道拥塞,在典型高密度OBUs数据交互场景下,安全信标的传播及时性和高速数据的传输成功率PDR都有所提高.

基于深度学习的海杂波谱参数预测与影响因素分析

该文基于不同雷达参数和海洋环境参数条件下的岸基雷达海杂波实测数据,利用深度神经网络(DNN)建模技术,建立了从多个测量条件参数出发的海杂波多普勒谱参数预测模型,实现了独立于杂波数据、基于环境特征的海杂波谱特征认知,谱频移和展宽的预测精度达90%以上。基于该预测模型,该文提出了一种基于参数循环递减认知的多普勒谱影响因素分析方法,分析了不同测量参数对海杂波多普勒谱预测的影响,得到了谱参数随主要影响因素的变化规律,结果对基于多普勒特征的海面目标检测应用具有重要意义。